Trapping of oxygen vacancy at grain boundary and its correlation with local atomic configuration and resultant excess energy in barium titanate: A systematic computational analysis

Atomic structures of (001) symmetric tilt grain boundaries (GBs) and their influences on the trapping of oxygen vacancies at GBs in barium titanate (BaTiO(3)) were analyzed using static atomistic simulation techniques. It is found that the structures are determined to minimize the deficiency in the coordination numbers of Ti(4+) ions and to suppress the structural distortion in the vicinity of the GBs. The excess energy of the GB is dependent on the number density of the coordination-deficient Ti(4+) ions, indicating that the ionic bonds between Ti(4+) and O(2-) ions are responsible for structural stabilization of GB. It is also found that the GB plays an important role in trapping oxygen vacancies, which acts as a resistance against the oxygen vacancy's diffusion. The trapping originates from the presence of irregular O(2-) sites, where oxygen vacancies energetically prefer to reside, influenced by coordination environment. Based on the detailed analyses on origins of GB energy and the trapping in the vicinity of GB, new physical ground that correlates GB energy and capability of oxygen-vacancy trapping are provided, enabling us to predict how much vacancies can be trapped at GBs on the atomic level by micrometer-order measurement of GB energy. Electrical degradation of the BaTiO(3) dielectrics used for multilayer ceramic capacitors can be prevented through controlling the characteristics of the GBs to promote oxygen-vacancy trapping at GBs in polycrystalline materials via modifying materials synthesis procedures.